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Hi Stephen & All, Nov 17, 2011
Shainberg et al., 1989 Use of gypsum on soils: a review. Pages 1-111 in
B.A.Stewart, ed. Adv.in Soils Sci. Vol 9, Springer-Verlag, N.Y. is a good
starting source. Gypsum is usually used either to supply calcium or improve
soil structure and drainage, especially of saline soils.
Gypsum, as you suppose, does not act as a buffer. Depending upon soil
composition, soil physical properties and biotic factors, it variously
increases soil pH, decreases soil pH or has no effect. These effects can
sometimes be predicted in hindsight and are always small relative to rate.
In one orchard trial, I applied a total of 6 kg/m^2 of gypsum to a 10
square metre area under each tree (60 kg/tree) over a period of 5 years and
this caused a small uniform decrease in pH throughout the profile sampled (7
levels, 0-100 cm; p<0.001); Control pH 5.84, Coarse Gypsum 5.57, Fine Gypsum
5.49 (Table 35, Webster, D.H., 1999, Tech. Pub. 99-02).
Yt, Dave Webster, Kentville
----- Original Message -----
From: "Stephen R. Shaw" <srshaw@dal.ca>
To: <naturens@chebucto.ns.ca>
Sent: Wednesday, November 16, 2011 11:37 PM
Subject: Re: [NatureNS] Fundy gypsum
> The comments below seem puzzling at first sight.
>
> Reflecting DW's comment (who seems to be knowledgeable about soil
> chemistry), how is it that CaSO4.2H2O (gypsum) could act as a buffer for
> anything? Calcium sulphate dihydrate is slightly soluble in water, and
> neither the completely dissociated Ca or SO4 ions produced from the salt
> in solution would be expected to have buffering properties, or am I
> missing something? Is it that the calcium releases something from its
> interaction with some soil component, and that this indirect effect can
> then produce some buffering? Gypsum apparently has been used, in the
> past at least, to enhance crop growth (wheat), but I'm guessing that this
> effect could be due to fertilizing supplementation of either low calcium
> or low sulphate (calcium is involved in lots of cell functions) --
> something other than buffering.
>
> It would be interesting to hear some detail on both counts: how any
> buffering effect from dissolved gypsum is thought to come about, and how
> agricultural application of gypsum can sometimes increase crop yield.
> Maybe someone knows?
> Steve, Halifax
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Quoting Doug Linzey <doug.linzey@gmail.com>:
>> On 15/11/2011 7:38 PM, Dusan Soudek wrote:
>>> As minerals go, gypsum is probably environmentally the most benign
>>> one there is. It even neutralizes the acid rain that is ruining our
>>> Atlantic salmon, speckled trout, and other fish populations.
>>
> (& Doug Linzey wrote) If you have to have a mine in your back yard,
> gypsum would be a good choice. It's a pretty benign mineral. The walls of
> our houses are made of it. It's in some of the food we eat. It's a common
> soil additive. And to address Dusan's last point, it is a salt with
> buffering properties: it can raise the pH of acidic soils and lower the
> pH of alkaline soils...
>
>
>
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